The present invention relates generally to rotatable members that are able to achieve balanced conditions throughout a range of rotational speeds. The present invention also relates to methods and systems for dynamically balancing rotatable members through the continual determination of out of balance forces and motion to thereby take corresponding counter balancing action. The present invention additionally relates to methods and system for improving control model updates applied to dynamic balancing.
Mass unbalance in rotating machinery leads to machine vibrations that are synchronous with the rotational speed. These vibrations can lead to excessive wear and to unacceptable levels of noise. Typical imbalances in large, rotating machines are on the order of one inch-pound.
It is a common practice to balance a rotatable body by adjusting a distribution of moveable, inertial masses attached to the body. This state of balance may remain until there is a disturbance to the system. A tire, for instance, can be balanced once by applying weights to it. This balanced condition will remain until the tire hits a very big bump or the weights are removed. However, certain types of bodies that have been balanced in this manner will generally remain in balance only for a limited range of rotational velocities. A centrifuge for fluid extraction, however, can change the amount of balance as more fluid is extracted.
Many machines are also configured as freestanding spring mass systems in which different components thereof pass through resonance ranges, during which the machine may become out of balance. Additionally, such machines may include a rotating body loosely coupled to the end of a flexible shaft rather than fixed to the shaft as in the case of a tire. Thus, moments about a bearing shaft may also be created merely by the weight of the shaft. A flexible shaft rotating at speeds above half of its first critical speed can generally assume significant deformations, which add to the imbalance. This often poses problems in the operation of large turbines and turbo generators.
Machines of this kind usually operate above their first critical speed. As a consequence, machines that are initially balanced at relatively low speeds may tend to vibrate excessively as they approach full operating speed. Additionally, if one balances to an acceptable level rather than to a perfect condition (which is difficult to measure), the small remaining xe2x80x9cout-of-balancexe2x80x9d will progressively apply greater force as the speed increases. This increase in force is due to the fact that F is proportional to rxcfx892 (note that F is the out of balance force, r is the radius of the rotating body and xcfx89 is its rotational speed).
The mass unbalance distributed along the length of a rotating body gives rise to a rotating force vector at each of the bearings that support the body. In general, the force vectors at respective bearings are not in phase. At each bearing, the rotating force vector may be opposed by a rotating reaction force, which can be transmitted to the bearing supports as noise and vibration. The purpose of active, dynamic balancing is to shift an inertial mass to the appropriate radial eccentricity and angular position for canceling the net unbalance. At the appropriate radial and angular distribution, the inertial mass can generate a rotating centrifugal force vector equal in magnitude and phase to the reaction force referred to above.
Many different types of balancing schemes are known to those skilled in the art. When rotatable objects are not in perfect balance, nonsymmetrical mass distribution creates out-of-balance forces because of the centrifugal forces that result from rotation of the object. Although rotatable objects find use in many different applications, one particular application is a rotating drum of a washing machine.
U.S. Pat. No. 5,561,993, which was issued to EIgersma et al. on Oct. 22, 1996, and is incorporated herein by reference, discloses a self-balancing rotatable apparatus. Elgersma et al. disclosed a method and system for measuring forces and motion via accelerations at various locations in a system. The forces and moments were balanced through the use of a matrix manipulation technique for determining appropriate counterbalance forces located at two axial positions of the rotatable member. The method and system described in Elgersma et al. accounted for possible accelerations of a machine, such as a washing machine, which could not otherwise be accomplished if the motion of the machine were not measured. Such a method and system was operable in association with machines not rigidly attached to immovable objects, such as concrete floors. The algorithm disclosed by Elgersma et al. permitted counterbalance forces to be calculated even when a washing machine is located on a flexible or mobile floor structure combined with carpet and padding between the washing machine and a rigid support structure.
U.S. Pat. No. 5,561,993 thus described a dynamic balance control algorithm for balancing a centrifuge for fluid extraction. To accomplish such balance control, sensor responses to balancing control actions on a centrifuge may be modeled and utilized to determine control actions to drive an associated system toward a balanced state. Such a system is generally time variant, such that the control models utilized therein can be routinely updated based on the measured response to a previous control action, which is a variation of perturbation theory, well known in the art. The control algorithm explained in U.S. Pat. No. 5,561,993 simply updated the control models after every designated control action. The present inventors realize, however, that such a control method can lead to unneeded model updates or the creation of poor models resulting in inadequate predictions. This in turn can lead to lengthy balancing times and the inability to obtain maximum spin speeds in centrifuge environments, such as, for example, a clothes washing machine.
The present inventors have thus concluded that previous methods for dynamically balancing a rotatable member have experienced severe limitations in the degree of balance that can be achieved and in the rotational speeds under which they operate. The present inventors conclude that it would be desirable to recognize when existing control models for balancing loads are no longer performing well. The present inventors also believe that it would be desirable to recognize when the results of a previous control action are adequate to support a control model update, and thereby provide a basis for updating the control model in a timely fashion to ensure that the control model sufficiently represents the system requiring balancing. The present inventors have additionally concluded that it would be desirable to implement methods and systems for computing new test actions that are based on information obtained from the system rather than applying random perturbations to the system at each new speed or when it is confirmed that the control action is not having the desired affect. The invention disclosed herein thus addresses these needs.
The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to the present invention and is not intended to be a full description. A full appreciation of the various aspects of the invention can be gained by taking the entire specification, claims, drawings, and abstract as a whole.
It is one aspect of the present invention to provide methods and systems in which rotatable members can achieve balanced conditions throughout a range of rotational speeds.
It is another aspect of the present invention to provide methods and systems for dynamically balancing rotatable members through the continual determination of out-of-balance forces and motion to thereby take corresponding counter balancing action.
It is still another aspect of the present invention to provide methods and systems for improving control model updates applied to dynamic balancing.
In accordance with various aspects of the present invention, methods and systems are disclosed herein for dynamically updating a control model for controlling a balance state of a rotating device or rotating system. Sensor responses can be utilized to define a control model that, along with sensor measurements, can be used to determine control actions that drive the rotatable apparatus to a balanced state and provide new sensor responses. Recognizing when an existing control model is no longer performing well, and when the results of a previous control action are adequate to support a control model update, a basis is provided for updating the control model in a timely fashion and ensuring that it sufficiently represents the rotatable apparatus. A global or aggregate metric, along with a sensor distribution metric, may be calculated from sensor measurements and evaluated to determine if it is necessary to update the control model and to determine if the recent sensor response is sufficient to update the control model. The performance of the control model may be evaluated utilizing rate of change data obtained by evaluating sensor measurements from one control action to the next. When prior control actions are not adequate for control model update, or the system experiences a significant operational change, forced control actions (test actions) may be computed with the intent of moving along the anticipated best balance-control trajectory and doing this with two sufficiently different control actions so as to provide sufficient system response for a control model update. The collection of these methods and systems ensure timely control model updates for an accurate control model under changing system conditions, thereby improving balance times and enhancing the achievement of maximum spin speeds in a rotating system. Similar techniques may be utilized to determine whether or not a balanced state (i.e., threshold) has been met or exceeded.
The present invention thus makes possible an improved dynamic balancing procedure that accounts for both forces and motion that may be imposed on a rotating member or rotating apparatus, such as the drum of a washing machine.